TraceMonkey was not included in alpha versions of Firefox 3.1, but was available in nightly builds but now, it has been integrated into the FireFox 3.1 release. That said, it is still disabled by default. In order to enable it, you have to set the javascript.options.jit.content variable in about:config to true, and restart the browser. The developers Andreas Gal and Michael Franz give details of TraceMonkey in their blog.

Firefox 3.1 Beta 1 also contains the previously announced Geolocation support. The HTML5 video and audio elements are also enabled with Firefox currently supporting Ogg Theora and Ogg Vorbis formats. Mozilla's developers aim to make it just as easy to publish a video or an audio file as an image.

Further details about the new features in Firefox 3 Beta 1, such as support for @font-face, XHR extensions, a new tab switcher with previews and improved support for web standards in the Gecko rendering engine, are given in an overview for web developers. The release notes provide a more general introduction to Firefox 3.1 Beta 1 while the developer site for Firefox 3.1 details what features are planned for the final release which have not made it to the beta 1 release.

Firefox 3.1 Beta 1 is specifically for testing purposes and the developers recommends that it is not used for production or daily user. It is available for Windows, Mac OS X and Linux and is available to download in various languages. There will be a number of other betas released before the final Firefox 3.1 which is due by the end of the year.